Earth moving machinery, both wheel and track-driven, operate on a variety of surface types and grades. Moreover, such machinery is subject to an acceptable level of slipping while attempting to dig into or move material. Continuous track machines are a class of earth moving machinery (e.g., bulldozers, earth movers, etc.) where the machine propulsion/ground interface is a continuous band of joined metal plates. The continuous band of plates is driven by two or more wheels/sprockets. The large surface area of the tracks distributes the weight of the vehicle over a greater surface area than wheel-propelled machinery. The continuous track machines are thus generally able to traverse soft (e.g., muddy) ground more easily than wheeled machinery that would likely get stuck in relatively soft ground. Traction is enhanced on continuous track machinery by the presence of prominent metal ridges extending from the metal plates. The pronounced ridges/treads of the continuous track plates provide good traction in soft surfaces. Continuous track machines are commonly used on a variety of vehicles today, including bulldozers and excavators. However, continuous tracks can be found on any vehicle used in an application that can benefit from the added traction, low ground pressure and durability inherent in continuous track propulsion. Other earth moving machinery (e.g., a wheel loader) is equipped with large wheels with wide treads for providing extra traction in potentially soft ground.
Hydraulic machines are driven by fluid pressure. Examples of such machinery include wheel loaders, bulldozers and other continuous track driven machinery. In hydraulic machines, hydraulic fluid is transmitted to hydraulic motors and hydraulic cylinders, and the fluid becomes pressurized according to a resistance present in the motors/cylinders. The fluid is controlled directly or automatically by control valves and distributed throughout the machinery by hoses and tubes. A fundamental feature of hydraulic systems is the ability to apply a potentially very large force, through force multiplication, in a relatively easy way by appropriately sizing effective area of connected cylinders or effective displacement (volume per pump revolution) between a pump and a motor (sometimes referred to as transmission or displacement ratio). Given the potentially very large forces generated by hydraulically driven machinery, loss of traction is inevitable. When traction is lost between the physical drive interface between the machinery and the ground, power output and force are decreased to stop the slipping condition.
It is useful to determine when an excessively large amount of slippage occurs at a drive interface between a machine and a surface (e.g., the pavement, ground, etc.) upon which the machine travels. In wheel driven machines, known anti-slip mechanisms (during acceleration) compare drive wheel and driven wheel speeds to detect/measure actual slippage and reduce torque demand when excessive slippage is detected. See e.g., Phelps et al., U.S. Pat. No. 4,521,856 and Schafer et al, U.S. Pat. No. 5,696,683. Such comparisons are unavailable in the case of continuous track machines that have only drive tracks.
This and other shortcomings in the state of the art are addressed by aspects of an exemplary method and transmission assembly (including a controller thereof) described herein.